Steam cooling of alkylate fractionator



Nov. 26, 1968 J, KUNESH STEAM COOLING oF ALKYLATE FRAcTIoNAToR Filed OCT.. 2C), 1966 S :GSW

N Mm MR Ea .T N Y. /M A 5X; may@ HIJ? United States Patent O 3,413,217 STEAM COOLING 0F ALKYLATE FRACTIONATOR John G. Kunesh, Arlington Heights, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Oct. 20, 1966, Ser. No. 588,133 11 Claims. (Cl. 208-356) ABSTRACT 0F THE DISCLOSURE Method for preventing excessive temperature increase during the distallation of crude alkylate. The crude alkylate is introduced into a distillation zone to separate products comprising detergent-grade alkylate and heavy alkylate. Steam is introduced into the distillation column only when the measured or desired temperature exceeds a predetermined level.

This invention relates to the fractionation of hydrocarbons. It particularly relates to a method for preventing excessive temperature increase during the distillation of particular hydrocarbons. The invention particularly relates to a method for improving the sulfonating characteristics of monoalkylbenzenes.

The synthetic detergent industry is primarly based upon utilizing alkylbenzenes which have been suitable sulfonated in order to impart sufficient wetting properties to the chemical. Typical of the alkylbenzenes which have been used by the prior art, are those described in United States Patent No. 2,477,383. This prior art process prepares alkylbenzenes -by polymerizing lower olefins, such as propylene and butylene, to produce polymer :fractions containing 8 to 18 carbon atoms per polymer molecule. This polymer is then alkylated with benzene using a acid catalyst and the alkylation reaction mixture is suitably fractionally distilled to separate the detergent grade alkylate from the non-detergent grade alkylate products. For example, in such a distillation lower alkylbenzenes containing, for example, from 4 to 7 carbon atoms in the alkyl side chain, and the higher alkylbenzenes and dialkylbenzenes are separated from the monoalkylbenzenes.

The detergent industry has enjoyed a fair amount .of commercial success using alyklates produced in the abovedescribed manner. However, stringent property requirements have been placed on the industry for the quality of the alkylbenzenes which are used in the sulfonation reaction. The alkylbenzenes must yield a sulfonate which is essentially pure white in color, which is free from cracked or kerosene-like odor, and which is extremely low in residual sulfonated oil. lf these stringent property requirements are not met, the ultimate sulfonates are of lower quality than those demanded by the industry for the detergent business.

Therefore, it is an object of this invention to provide an improved fractionation method.

It is another object of this invention to provide a method for preventing excessive temperature increase during the distallation of a feedstock containing detergent-grade alkylate and heavy alkylate.

lt isstill another object of this invention to provide a method for improving the sulfonating characteristics of monoalkylbenzenes.

It is a particular object of this invention to provide a control method during the distillation of crude alkylate whereby abnormal increases and decreases in temperature during the distallation are avoided.

The invention will be presented in detail hereinbelow with reference to the appended drawing which is a schefrnatic rep-resentation of one embodiment of this invention.

ICS

According to the present invention, a method for preventing excessive temperature increase during the distillation of crude alkylate to separate detergent-grade alkylate and heavy alkylate comprises subjecting said crude alkylate to distillation in a distillation zone in the presence of steam and under conditions suliicient to produce a distillate fraction comprising detergent-grade alkylate and water, separating the water from said detergent-grade alkylate, heating separated water to produce steam therefrom, measuring a temperature within said zone, introducing said steam into said zone only when the measured temperature exceeds a predetermined level, and discontinuing the introduction of said steam only when the measured temperature decreases to about said predetermined temperature level.

Another embodiment of this invention provides a method for preventing excessive temperature increase during the distillation of a feedstock containing detergentgrade alkylate and heavy alkylate which comprises the steps of (a) passing said feedstock in the presence of steam into a distillation zone at a temperature sufficient to substantially vaporize mainly said detergent-grade alkylate; (b) removing heavy alkylate in high concentration as a residue stream; (c) introducing into said zone hereinafter specied additional amounts of steam at a locus intermediate to the feed point and the bottom of said zone only when the temperature within said zone increases abnormally above said temperature; (d) removing detergent-grade alkylate and steam as a distillate stream; (e) condensing said distillate stream to produce a hydrocarbon fraction comprising detergent-grade alkylate and an aqueous stream; (f) heating vsaid aqueous stream to produce steam an injecting at least a portion of such stream into the distillation zone as specified in step (c), and, (g) discontinuing the introduction of said additional steam only when the temperature within said zone decreases to said temperature.

Still another embodiment of this invention provides a method for improving the sulfonating characteristics of monoalkylbenzenes having alkyl side chains from 8 to 1S carbon atoms which comprises fractionally distilling crude alkylate in the presence of steam in a distillation zone under conditions sufficient to separate a distillate fraction comprising said monoalkylbenzene and Water and a residue fraction comprising heavy alkylate; separating the water from the monoalkylbenzenes; heating said water under conditions suflicient to produce steam therefrom; measuring a temperature within said zone; introducing at least part of said steam in response to said temperature measurement whereby abnormal temperature changes are avoided; and recovering monoalkylbenzenes in high concentration.

A specific embodiment of the invention includes controlling the amount of steam so introduced responsively to the change in said measured temperature.

It is to be noted from the recitation of the above embodiments and from the discussion presented herein, that the present invention is based upon the concept that distilling crude alkylate in the presence of steam could be considerably improved by injecting additional steam into the bottom of the tower only in response to a temperature change such that degradation of the detergentgrade alkylate would occur if the temperature were allowed to increase above a predetermined level. It was discovered that alkylates of the nature referred to herein are thermally unstable and the instability leads to a degradation of the detergent-grade alkylate and ultimately produces an inferior lgrade sulfonated product. Therefore, when the temperature Within the distillation zone increases above a predetermined level, additional amounts of steam are injected thereby dropping the hydrocarbon tillation step.

For the practice of this invention, one of the preferred classes of starting materials are the polypropylene polymer alkylates of benzene and toluene which may be formed by reacting a propylene polymer, such as a tetramer fraction, with benzene or toluene in the presence of an alkylation catalyst of the acid-acting type which produces an alkylate capable of 'being converted into the corresponding sulfonated product. The alkyl substituents on the ring may be made up of several short-chain alkyl groups, such 'as methyl, ethyl, propyl, and the like, in addition to the long-chain alkyl group containing from 8 to 18 carbon atoms respectively. 'Ihose skilled in the art are familiar with the methods of alkylating benzene and toluene to produce the crude alkylate material for the practice of this invention.

In the prior art it was conventional to distill the crude alkylate such that the detergent-grade alkylate was removed, preferably under vacuum, in the presence of steam as a distillate fraction. The rejected alkylate material, commonly called heavy alkylate, and including dicyclic aromatic materials, are generally removed from the bottom of the distillation zone. Since the crude alkylate contains temperature sensitive constituents, it is the preferred practice Iof this invention to carry out the distillation at atmospheric or sub-atmospheric pressure. In addition, the use of steam during the distillation to reduce the hydrocarbon partial pressure is also effective in minimizing the risk of thermal degradation of the alkylate product.

Referring now to the appended drawing, crude alkylate containing detergent-grade alkylate and heavy alkylate, is passed via line 10 into distillation column 11. The distillation conditions maintained in column 11 include, for example, an overhead temperature of approximately 455 F. and a bottoms temperature of approximately 480 F. Sub-atmospheric pressures are imposed on the column; for example, the top of the column may be 50 mm. Hg absolute pressure, while the bottom of the column is 150 mm. Hg. absolute pressure. The heavy alkylate is removed from the distillation column Via line 12. A distillate fraction comprising detergent-grade alkylate and water vapor in the form of steam is removed from column 11 via line 13 and passed into separator 14. By cooling means not shown, the temperature in separator 14 is reduced to, for example, 90 F., wherein the hydrocarbons therein are condensed as well as the steam. The :liquid detergent alkylate product is removed from separator 14 by line 15 and suitable amounts are returned as reflux to column 11 via line 16 while the net detergent-grade alkylate product is removed from the system via line 17.

The Water layer in separator 14 is withdrawn via line 18 and passed preferably into steam generator 19 wherein steam is generated by heat exchange with, for example, hot oil entering and leaving the system via line 20.

Temperature controller recorder (TRC) 25 is used to measure the temperature, preferably, in the bottom of column 11. For purposes of this discussion, the predetermined temperature level is about 480 F. TRC 25 is suitably connected with valve means 24 placed in line 23. As the temperature in column 11 increases above the predetermined level of 480 F., TRC 25 senses the temperature and transmits a signal to valve 24 which then opens and allows steam to flow from steam generator 19 via lines 21 and 23. Any excess steam generated 4, in generator 19 is passed out of the system via lines 21 and 22 into, for example, the refinery steam system.

As soon as the temperature in column 11 drops below the predetermined temperature level of 480 F., TRC 25 again transmits an appropriate signal to valve 24 which begins to close thereby decreasing the amount of steam flowing into column 11 from steam generator 19.

By operating in this fashion, abnormal temperature rises in column 11 are easily and economically controlled, Additional economies of operation are embodied in the inventive process in the reuse of the condensed steam in the steam generator for control of the temperature in the column.

Temperature recorder controller 2S may be a thermocouple or other temperature-responsive device. The signals generated by such device are transmitted through appropriate means to valve 24. The amount of steam which is introduced into column 11 as a result of the opening of valve 24 depends upon the magnitude of the heat inhalance which the steam is introduced to correct. Preferably, valve 24 is automatically closed when the temperature in column 11 falls again to a suitable operating level.

It is within the contemplation of the present invention for a portion of the heavy alkylate removed from the system via line 12 to be passed through conventional reboiler means for the generation of heat necessary as part of the distillation conditions imposed on distillation column 11. In such event, it is preferred in the practice of this invention for TRC 25 to measure the eluent stream from the reboiler system and for the steam passing from steam generator 19 in line 23 to be physically admixed with such effluent leaving the reboiler, or physically admixed with the heavy alkylate stream passing into the reboiler. In this Way, immediate response to the temperature level sensed by TRC 25 is accomplished with a minimum of time delay on the system.

Obviously, other temperature measurements may be taken within column 11, and these are to be included within the scope of the present invention. However, it s distinctly preferred in order to maximize the quality of the detergent-grade alkylate separated, to measure the temperature at least in the lower portion of the distillation column and, preferably, measure the temperature of the heavy alkylate being reboiled in the bottom of distillation column 11.

It is to be noted that throughout the discussion of the present invention the use of the temperature recorder controller to control the amount of steam introduced in the column is no way to limit the invention as having steam being introduced only by this means. Clearly, for the distillation of crude alkylate, the presence of steam is preferred in the column. Therefore, as used herein, it is intended that TRC 25 controls the temperature within the distillation column by adding or subtracting steam from that amount normally present in the column to carry out the distillation process.

By operating the distillation column in accordance with the teachings of the present invention, it was found that upon fractionation the alkylate distilled in this manner showed considerable color improvement over the alkylate obtained if such control means were not used during the distillation step.

The invention claimed:

1. Method for preventing excessive temperature increase during the distillation of a feedstock containing detergent-grade alkylate `and heavy alkylate which comprises the steps of:

(a) passing said feedstock in the presence of steam into a distillation zone at a temperature suflcient to substantially vaporize mainly said detergent-grade alkylate;

(b) removing heavy alkylate in high concentration as Y a residue stream; Y

(c) introducing into said zone hereinafter specified additional amounts of steam at a locus intermediate to the feed point and the bottom of said zone only when the temperature within said zone increases abnormally above said temperature;

(d) removing detergent-grade alkylate and steam as .a

distillate stream;

(e) condensing said distillate stream to produce a hydrocarbon fraction comprising detergent-grade alkylate, and an aqueous stream;

() heating said aqueous stream to produce steam and injecting at least a portion of such steam into the distillation zone as specified in step (c); and,

(g) discontinuingy the introduction of said additional steam only when the temperature within said zone decreases to said temperature.

2. Method according to claim 1 wherein said amount of steam introduced in controlled responsively to the change in said temperature.

3. Method according to claim 1 wherein said detergentgrade alkylate comprises monoalkylbenzenes having alkyl side chains containing from 8 to 18 carbon atoms.

4. Method for improving the sulfonating characteristics of monoalkylbenzenes having alkyl side chains from 8 to 18 carbon atoms which comprises fractionally distilling crude alkylate in the presence of steam in a distillation zone under conditions suiiicient to separate a distillate fraction comprising said monoalkylbenzene and water, and a residue fraction comprising heavy alkylate; separating the water from the monoalkylbenzenes; heating said Water under conditionss sufficient to produce steam therefrom; measuring a temperature within said zone; introducing at least part of said steam in response to said temperature measurement whereby abnormal temperature changes are avoided; and, recovering monoalkylbenzenes in high concentration.

5. Method according to claim 4 wherein said measured temperature is the temperature of the heavy alkylate so separated.

6. Method according to claim 5 wherein said measure temperature is less than 480 F.

7. Method according to claim 4 wherein heavy alkylate 4 is reboiled as part of said distillation conditions and the temperature so measured is the temperature of the effluent from the reboiler.

8. Method according to claim 7 wherein Said steam is introduced only when the measured temperature exceeds a predetermined temperature of about 480 F. and is discontinued only when the measured temperature decreases below said predetermined temperature.

9. Method for preventing excessive temperature increase during the distillation of crude alkylate to separate detergent-grade alkylate and heavy alkylate which comprises subjecting said crude alkylate to distillation in a distillation zone in the presence of steam and under conditions sufficient to produce a distillate fraction comprising detergent-grade alkylate and water; separating the water from said detergent-grade alkylate; heating separated water to produce steam therefrom; measuring a ternperature within said zone; introducing at least part of said steam into said zone only when the measured temperature exceeds a predetermined level; and, discontinuing the introduction of said steam only when the measured temperature decreases to about said predetermined temperature level.

10. Method according to claim 9 wherein said conditions include sub-atmospheric pressure.

11. Method according to claim 10 wherein said predetermined temperature level is about 480 F.

References Cited UNITED STATES PATENTS 1,587,188 6/1926 Schneible 203-2 1,601,320 9/1926 Peters 202-160 2,995,611 8/1961 Linn et al 260-671 3,003,943 10/ 1961 Little 202--160 3,126,422 3/ 1964 Planchard 260-671 2,282,982 5/1942 Jewett 196-134 2,525,276 10/1950 Shapleigh 208--130 3,353,920 11/1967 Kitzen 208-130 0 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Assistant Examiner. 

